This book chronicles the details of a global-scale, systematically geographically gridded, process-based crop simulation modeling system developed at IFPRI in support of global-scale economic models of agriculture. An endeavor such as this necessarily entails many steps, assumptions, and obscure minutia. Outside observers and users of the results rightly question how the final numbers came about and whether some step had an undue or incorrect influence on the outcomes. Researchers engaged in similar or allied pursuits may wish to make use of such a system or build one of their own from the ground up.